One way to resolve the problem of coincidence (or, at least ameliorate it to a certain degree)
is to make allowance for interaction(s) between the DE and DM components
[1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}.
However, these
components being so different in character, the physical realization of such interactions is
often very difficult, unless they appear naturally, for e.g. via conformal transformations in
the scalar-tensor formulations of gravitational theories
[9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [15]}, [16]}.
A more robust approach therefore is to bring a unified dark sector in the reckoning,
i.e. to consider a scenario in which the DE, the DM, and possibly certain interaction(s)
thereof, all having the same fundamental origin
[17]}, [18]}, [19]}, [20]}, [21]}.
Of course, in that way the DE and the DM would lose their individuality, and would merely
be the structural artefacts of the source, which thereby would become the all-important
entity that shapes up the evolution profile of the cosmological dark sector.
